Method of and apparatus for regulating the resistance of film resistors

ABSTRACT

Method and apparatus for automatically trimming film resistors in production quantities. The method includes the steps of placing a substrate with a film resistance to be trimmed on a support beneath a grid mask of desired pattern; extending fiber optics from the grid mask to a fiber optic receiving support; directing a laser beam towards the receiving support; and moving the receiving support relative to the beam in a controlled manner. Apparatus may include a support table for supporting a substrate carrying a film to be trimmed in position to be in contact with a set of electrical probes connected with a sensor circuit for monitoring the actual resistance value of the film. Positioned above the film and substrate is a fixed aperture mask carrying the geometric requirements of the circuit with openings at required precision adjustment points. A fiber optic pipe joins each opening so as to focus light conducted by the fiber optic in the thin film plane of the resistor matrix. The fiber optic light pipes terminate in a common plane to receive a laser beam. The receiving end of the fiber optic light pipes and the laser beam are movable relative to one another so that the beam may be directed to select pipes. The relative movement is controlled dependent upon the desired pattern and actual monitored resistance value.

United States Patent McWillianis [54] METHOD OF AND APPARATUS FORREGULATING THE RESISTANCE OF FILM RESISTORS [72] Inventor: Donald A.McWilliams, 1916 North Gilbert, Fullerton, Calif. 92633 [22] Filed: Nov.5, 1969 [2]] Appl.No.: 874,227

[521 US. Cl. ..29/610, 29/620, 219/121 L, Y 5 350/96 R 51 1m. (:1...llOlc 17/00 [58] Field of Search...'. ..29/610, 620,121 L, 121 E13;350/96 R [56] References Cited UNITED STATES PATENTS 3,382,343 5/1968Muncheryan ..219/121 3,383,491 5/1968 Muncheryan ..219/121 3,388,4616/1968 Lins ..29/620 x 3,534,472 10/1970 De Jong et al ..29/ 203,535,778 10/1970 Falanga et al. ..29/610 Primary Examiner-John F.Campbell Assistant Examiner-Victor A. Di Palma Attorney-Jack M. Wisemanand Thomas E. Schatzel Oct. 24, 1972 [57] ABSTRACT Method and apparatusfor automatically trimming film resistors in production quantities. Themethod includes the steps of placing a substrate with a film resistanceto be trimmed on a support beneath a grid mask of desired pattern;extending fiber optics from the grid mask to a fiber optic receivingsupport; directing a laser beam towards the receiving support; andmoving the receiving support relative to the beam in a controlledmanner. Apparatus may include a support table for supporting a substratecarrying a film to be trimmed in position to be in contact with a set ofelectrical probes connected with a sensor circuit for monitoring theactual resistance value of the film. Positioned above the film andsubstrate is a fixed aperture mask carrying the geometric requirementsof the circuit with openings at required precision adjustment points. Afiber optic pipe joins each opening so as to focus light conducted bythe fiber optic in the thin film plane of the resistor matrix. The fiberoptic light pipes terminate in a common plane to receive a laser beam.The receiving end of the fiber optic light pipes and the laser beam aremovable relative to one another so that the beam may be directed toselect pipes. The relative movement is controlled dependent upon thedesired pattern and actual monitored resistance value.

18 Claims, 3 Drawing Figures 4 SUBSTRATE 1 i SUPPORT TABLE J2 PATENTED E24 I972 3,699,649

32 30 d a DRIVER d COMMAND it v I7 SENSOR SUBSTRATE 1 SUPPORT TABLE 2 2sF|G.2 I02 ,30' 32 F LASER I: 1 DRIVER DRIVER T COMMAND l8 L 1 SENSOR I00A SUBSTRATE SUPPORT TABLE J I00 I 28' 24' Joz ,30 i -32 *='J;--- DRIVEREij" :EDR'VER COMMAND INVENTOR F|G 3 DONALDAMcWILLIAMS BYylu n UMATTORNEYS METHOD OF AND APPARATUS FOR REGULATING THE RESISTANCE OF FILMRESISTORS BACKGROUND OF THE INVENTION 'The present invention relates toregulating the value of film resistors in the manufacturing process.I-Ieretofore, there have been various techniques utilized for regulatingthe values of thick film and thin film resistors. Such techniques aretime consuming and incorporate expensive equipment. A particulartechnique may include a laser optical system aimed at a fixed point inspace. A resistor for trimming is placed beneath the laser at the focalpoint of the laser. This resistor is positioned either manually or bysome motor driven automatic or semi-automatic mechanical table. Afterthe resistor is in place, probes are lowered on the resistor or otherelectrical connections are made. The electrical connections extend to abridge circuit including a sensor within the system to determine theresistance value of the resistor. The laser trimming operation thenbegins. The laser cuts away portions of the resistor at the focal pointincreasing the effective resistance of the resistor. This technique isgenerally recognized as being time consuming and expensive. Inparticular, the mechanical table used to position the complex substrateis relatively expensive in cost as it requires considerable precision tolocate the resistor and this precision must be available for severalinches of substrate distance. The relatively high degree of cost andtime consumption may be attributed to it being a mechanicalinconsistency to require high speed operation over a long distance whilesimultaneously obtaining great precision in the final location of thetable. For example, in the prior art applications, it is generallyrequired that precision of a thick film resistor substrate be withintwoor three-thousands of an inch. Obviously, these requirements aredifficult to realize without incurring excessive time and expense.

SUMMARY OF THE PRESENT INVENTION The present invention teaches a methodand apparatus which isolates the technique of precision location fromthe high speed stepping function and eliminates the necessity of aprecision mechanical table. The method and apparatus herein is adaptedto provide low cost, high production, fully automatic precisionadjustment of thick film and thin film resistor substrates. The resistorsubstrate may be either a pan of an electronic integrated circuit or adiscrete individual component.

In an exemplary embodiment, the resistor substrate with film to beregulated is positioned on a mechanical table preferably by automaticfeed machinery. The substrate is then positioned on the table to engagea set of probes which extend to a monitor sensing network for monitoringthe resistance value during adjustment. A

mask of a grid pattern based on the geometric requirements of thedesired circuit of the film is positioned above the substrate. The maskcarries openings at required precision adjustment points. Fiber opticcomponents with appropriate focusing characteristics are joined to thepoints and focus light conducted by the fiber optics. The location ofthe openings within the mask holding the fiber optic conductor can beset with precision utilizing optical and photoresist processingtechniques. The receiving ends of the fiber optic light pipes are thenaligned at a support in a single line to receive a laser beam. Thesupport at the receiving end of the light pipes is movable relative tothe beam, such that the receiving ends may be rapidly placed in sequenceby stepping or other procedures within the path of the laser beam suchthat individual pipes conduct light to the mask and on the film. Themoving sequence may be coordinated with a programed network whichpredetermines the final desired resistance value. The laser may bearranged to be responsive to the monitor circuit such that each resistoris individually and automatically trimmed to its final desired value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates diagrammaticallyapparatus incorporating the teachings of the present invention and shownin conjunction with a resistor.

FIG. 2 illustrates a modification of the apparatus shown in FIG. 1 whichalso embodies the teachings of the present invention.

FIG. 3 illustrates a-top view of the apparatus shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 diagrammaticallyillustrates apparatus for practicing the teachings of the presentinvention. The apparatus, referred to by the general reference character10, comprises a mechanical support table 12 for receivinga substrate 14with a resistance film 15, the resistance value of which is to beregulated. The table 12 may be designed to be raised and lowered suchthat after the substrate 14 is placed on the top of the table 12 it maythen be raised by automatic feed machinery to contact a set of probes 16adapted to provide electrical connection between the thin film substratecircuit and an internal sensor network 17 adapted to provide a readingand monitor the resistance value of the film circuit on the substrate.Immediately above the probes 16 is a fixed aperture mask 18 having apattern based on the the geometric pattern requirements of the desiredcircuit. The mask generally carries an opening 20 at each requiredprecision adjustment point to be assumed by the film. Into each of theopenings 20 is inserted an optical fiber component 22 with appropriatefocusing characteristics to focus conducted light in the plane of theresistor substrate 14. The location of the openings 20 within the mask18 can be as precise as optical techniques and photoresist processingpermit. For example, precision better than micro inches may be readilyrealized. The fiber optic light pipes 22 or other suitable light pipesare then gathered at their respective receiving ends at a support member24 forming a common plane parallel to the mask 18. The support member 24carries a plurality of apertures 26 of centers spaced a distance d.Above the member 24 is a laser 28 generating a beam of a diameter dwhich is slightly less than the dimension d. The support 24 is designedto be movable laterally relative to the laser beam. The optic pipes areflexible sufficiently to be moved at their receiving ends such that thevarious select apertures 26 are aligned with the beam. The steps may berealized through simple mechanical techniques which need only be withina a precision of approximately one-sixteenth of an inch.

For example, the support 24 may be linked with a mechanical steppingdriver 30 which in turn is operatively responsive to a driver commandnetwork 32. Thus, the fiber optic receiving ends at the support 24 areplaced rapidly in sequence by stepping procedures beneath the laser beam28. The stepping operations coordinated by the driver command 32 whichmay be in the form of a tape program which predetermines the finaldesired resistor value of each resistor at each step. The sensor 17 iscoordinated with the command 32 and generates control signals forcontrolling the laser so that the resistor film on the substrate 14 isautomatically trimmed to its final desired value.

FIGS. 2 and 3 depict modified apparatus to further illustrate theteachings of the present invention and referred to by the generalreference character 100. Elements similar to those of FIG. I carry thesame reference numeral designated by a prime. In the ap paratus 100, thebeam from the laser 28' is directed in a plane parallel with the support24' and the mask 18'. The beam is directed at a mirror 102 positioned ata 45 angle relative to the beam and towards the support 24'. The beamfrom the laser 28 is diverted into the individual light pipes 22' by themirror 102. The mirror 102 may travel laterally and longitudinally abovethe fiber optic light pipes 22 and the support 24' so as to interceptthe laser beam and direct it into the top of specific pipes 22.Accordingly, during the trimming operation, only the mirror is moved.The movement of the mirror 102 may be controlled by the driver 30' andthe driver command 32' similar to the manner the support 24 iscontrolled in FIG. 1. The mirror 102 may be of light weight andcontrolled in a stepping fashion very rapidly with a minimum amount ofmechanical apparatus while the remainder of the apparatus is relativelystationary.

The above described invention provides versatile method and apparatusfor the trimming of film resistors in a manufacturing process. Thestepping operation of placing the beam relative to the substrate isisolated from the step of directing the beam onto the film itself. Theonly element that need be replaced in the system for different resistorsubstrates is the low cost aperture mask which locates the bottom end ofthe fiber optic light pipes. Fine trimming precision is realized whileproviding a more rapid operation and more economical operation over thatof methods heretofore known to the inventor. Due to the minimal numberof moving parts, mechanical failure is considerably reduced.

1 claim:

1. A method of trimming film resistors comprising the steps of:

placing a substrate with the film resistor to be trimmed on an articlesupport beneath a grid mask of a desired pattern, projecting a laserbeam toward a fiber optic receiving conducting the laser beam by fiberoptic means from the fiber optic receiving support to the grid mask forimpingement of the laser beam on the film resistor to trim the filmresistor, and

moving the fiber optic receiving support relative to the projectinglaser beam in a controlled manner for controlling the intensity of thelaser beam impinging on the film resistor.

2. The method of claim 1 and further including the step of monitoringthe resistance value of the film by sensing the resistance thereofthrough probes and a sensor network.

3. The method of claim 2 and further including the step of controllingthe intensity of the laser beam in response to a monitoring signal.

4. The method of claim 3 in which the receiving support and the beam aremoved relative to one another in discrete steps.

5. Apparatus for trimming film resistor comprising,

in combination:

a laser beam source for generating a laser beam,

a plurality of fiber optic means with receiving ends to receive thelaser beam,

a mask of a select grid pattern with a plurality of openings, each ofsaid openings receiving respectively one of said fiber optic means,

a support for supporting a film resistor substrate beneath and inalignment with the mask, and

means for imparting relative movement between the laser beam and saidreceiving ends of said plurality of fiber optic means.

6. The apparatus of claim 5 and including a support member forsupporting the receiving ends of said plurality of fiber optic means ina select format.

7. The apparatus of claim 6 in which the support member supports saidreceiving ends of the plurality of fiber optic means in an alignedpattern.

8. The apparatus of claim 7 in which I the support member supports saidreceiving ends of the plurality of fiber optic means in an alignedpattern with the spacing between centers of the openings exceeding thediameter of the beam.

9. The apparatus of claim 7 and further including a monitor formonitoring the resistance value of the film on said film resistorsubstrate by sensing the resistance thereof through probes and a sensornetwork.

10. The apparatus of claim 9 in which the monitor provides a controlsignal for controlling the intensity of the laser beam in response tothe resistance value of said film.

11. The apparatus of claim 10 and further including driver means formoving the support member across the laser beam in a controlled format.

12. The apparatus of claim 1 1 in which the driver means is adapted tomove the support member in discrete steps in response to a command.

13. The apparatus of claim 10 and further including mirror means forreceiving the laser beam and directing the laser beam toward the supportmember and the receiving ends of the plurality of fiber optic means.

14. The apparatus of claim 13 and further including driver means formoving the mirror means relative to the support member.

15. The apparatus of claim 14 in which the driver means is adapted tomove the mirror means in discrete steps relative to the support memberin response to command signals.

16. A method of trimming film resistors comprising the steps of:

placing a substrate with the film resistor to be trimmed on an articlesupport beneath a grid mask of a desired pattern,

projecting a laser bean toward an optic receiving support,

conducting the laser beam by optic means from the optic receivingsupport. to the grid mask for impingement of the laser beam on the filmresistor to trim the film resistor, and

moving the optic receiving support relative to the projecting laser beamin a controlled manner for controlling the intensity of the laser beamimpinging on the film resistor.

17 Apparatus for trimming film resistors comprising,

in combination:

in claim 17 wherein each of said optic means is an optic light pipe.

1. A method of trimming film resistors comprising the steps of: placinga substrate with the film resistor to be trimmed on an article supportbeneath a grid mask of a desired pattern, projecting a laser beam towarda fiber optic receiving support, conducting the laser beam by fiberoptic means from the fiber optic receiving support to the grid mask forimpingement of the laser beam on the film resistor to trim the filmresistor, and moving the fiber optic receiving support relative to theprojecting laser beam in a controlled manner for controlling theintensity of the laser beam impinging on the film resistor.
 2. Themethod of claim 1 and further including the step of monitoring theresistance value of the film by sensing the resistance thereof throughprobes and a sensor network.
 3. The method of claim 2 and furtherincluding the step of controlling the intensity of the laser beam inresponse to a monitoring signal.
 4. The method of claim 3 in which thereceiving support and the beam are moved relative to one another indiscrete steps.
 5. Apparatus for trimming film resistor comprising, incombination: a laser beam source for generating a laser beam, aplurality of fiber optic means with receiving ends to receive the laserbeam, a mask of a select grid pattern with a plurality of openings, eachof said openings receiving respectively one of said fiber optic means, asupport for supporting a film resistor substrate beneath and inalignment with the mask, and means for imparting relative movementbetween the laser beam and said receiving ends of said plurality offiber optic means.
 6. The apparatus of claim 5 and including a supportmember for supporting the receiving ends of said plurality of fiberoptic means in a select format.
 7. The apparatus of claim 6 in which thesupport member supports said receiving ends of the plurality of fiberoptic means in an aligned pattern.
 8. The apparatus of claim 7 in whichthe support member supports said receiving ends of the plurality offiber optic means in an aligned pattern with the spacing between centersof the openings exceeding the diameter of the beam.
 9. The apparatus ofclaim 7 and further including a monitor for monitoring the resistancevalue of the film on said film resistor substrate by sensing theresistance thereof through probes and a sensor network.
 10. Theapparatus of claim 9 in which the monitor provides a control signal forcontrolling the intensity of the laser beam in response to theresistance value of said film.
 11. The apparatus of claim 10 and furtherincluding driver means for moving the support member across the laserbeam in a controlled format.
 12. The apparatus of claim 11 in which thedriver means is adapted to move the support member in discrete steps inresponse to a command.
 13. The apparatus of claim 10 and furtherincluding mirror means for receiving the laser beam and directing thelaser beam toward the support member and the receiving ends of theplurality of fiber optic means.
 14. The apparatus of claim 13 andfurther including driver means for moving the mirror means relative tothe support member.
 15. The apparatus of claim 14 in which the drivermeans is adapted to move the mirror means in discrete steps relative tothe support member in response to command signals.
 16. A method oftrimming film resistors comprising the steps of: placing a substratewith the film resistor to be trimmed on an article support beneath agrid mask of a desired pattern, projecting a laser bean toward an opticreceiving support, conducting the laser beam by optic means from theoptic receiving support to the grid mask for impingement of the laserbeam on the film resistor to trim the film resistor, and moving theoptic receiving support relative to the projecting laser beam in acontrolled manner for controlling the intensity of the laser beamimpinging on the film resistor.
 17. Apparatus for trimming filmresistors comprising, in combination: a laser beam source for generatinga laser beam, a plurality of optic means with receiving ends to receivethe laser beam, a mask of a select grid pattern with a plurality ofopenings, each of said openings receiving respectively one of said opticmeans, a support for supporting a film resistor substrate beneath and inalignment with the mask, and means for imparting relative movementbetween the laser beam and said receiving ends of said plurality ofoptic means.
 18. Apparatus for trimming film resistors as claimed inclaim 17 wherein each of said optic means is an optic light pipe.